Treatment of fluidized oxidic iron ores to inhibit bogging



United States Patent 3,346,365 TREATMENT OF FLUIDIZED OXIDIC IRON (PRES T0 INHIBIT BOGGING Francis Xavier Mayer and Robert 0. Mask, Baton Rouge,

La., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Sept. 25, 1964, Ser. No. 399,386

14 Claims. (Cl. 7526) This invention relates to the production of sponge iron by reaction of oxidic iron cores by contact with reducing gases. In particular, it relates to an improved iron ore reduction process wherein fluidized iron ores are metallized by direct contact with hydrogen, carbon monoxide, or mixtures of these and other gases.

The invention contemplates incorporation of certain types of divalent sulfur compounds, in specific concentrations, into the reducing gas fed into a fluidized iron ore reduction process, particularly a staged fluidized iron ore reduction process having a discrete ferrous reduction stage, or stages, to inhibit bogging of the ore during reduction. The divalent sulfur compounds are characterized by the formula; R SR wherein R and R are selected from hydrogen and various monovalent organo radicals.

The production of sponge iron by reduction or oxidic iron ores, i.e., ore containing or consisting essentially of oxides or iron, in beds fluidized by upwardly flowing gases, at temperatures ranging generally from about 1000 F. to about 1800" F., is well known to the art. Moreover, such processess wherein the fluidized beds are staged as separate reduction zones, and the zones operated at the same of different elevated temperatures generally within this given range are also known.

In a typical staged fluidized iron ore reduction process, iron oxides are, e.g., provided: in a first fluidized bed wherein the oxides are reduced from the ferric state to magnetic oxide of iron; in a second fluidized bed wherein magnetic oxide of iron is reduced to ferrous oxide; and in a third zone wherein ferrous oxide is reduced to metal- =lic iron. The separate stages may be operated at the same or different elevated temperatures, and one of a plurality of ferric reduction zones or ferrous reduction zones may be provided. A burning zone wherein the reducing gas, e.g., hydrogen, is burned with an oxygencontaining gas, e.g., air, may be provided or the burning zone may be combined with a ferric reduction zone to provide heat for the reaction.

In all such process it is desired to have sufliciently high temperature to achieve maximum reduction, and to achieve such reduction smoothly and efl'iciently. One would expect to achieve maximum reduction by increasing the temperature of the reaction, and for the reaction to proceed at a faster rate with increasing temperature. However, high temperatures can produce bogging or, if the temperature becomes sufliciently high, sintering of the ore.

Bogging is a phenomenon manifested by a stickiness occurring at the surfaces of the individual solids iron ore particles. It is postulated, and fairly well supported, that the surfaces of the individual ore particles become covered, in whole or in part dependent on temperature, with crystalline forms of iron. These crystalline forms, micro scopic in character, take on the appearance of nodules or whiskers extending outwardly from the individual particles. The microscopic appearance of the individual ore particles with projecting deposits or nodular growths, in fact, is not too different from that of certain forms of vegetable or plant leaves which contain potassium oxalate or calcium carbonate growths. Because of these clawlike projections, or reactive spots, the particles tend to attach one to another upon contact so that individual iron ore particles cling or weld together to form aggr egates or agglomerates. Such phenomenon militates against proper fiuidization of the particles and hence bogging, or loss of fluidization of the bed occurs. This phenomenon is not unlike sintering of the particles in its effect but differs from sintering inasmuch as the latter is caused by an actual melting of the reduced iron upon the surfaces of the particles, this causing the individual particles to cling or fuse with another to also produce agglomeration.

Begging is a very undesirable phenomenon and the tendency of an ore to bog increases with metallization and with increasing temperature, especially as the degree of metallization increases. High temperatures ranging just below that which will produce sinteringi.e., about 1800 F.are desired, however, inasmuch as more efficient reduction and faster rate of reaction are achieved. This, then, presents a dilemma for, on the one hand, the higher the temperature the more acute the tendency toward bogging and, on the other, the lower the temperature the less the eflficiency of the process. With certain ores, e.g., Carol Lake ore, the tendency to bog at elevated temperature is especially severe, and for this reason it is diflicult to treat this and some other ores in a fluidized iron ore reduction process.

The present invention has for its primary objective a solution of the problem of bogging. In particular, its objective is to provide the art with a simplified, new and novel fluidized iron ore reduction process wherein bogging is inhibited and, in some cases, completely eliminated so that more elevated temperatures can be used and the process operated more effectively for longer periods. A specific object is to provide an improved process wherein the tendency toward bogging is inhibited or eliminated in the several stages of a fluidized iron ore reduction process wherein oxidic iron ores are treated with a reducing gas, or gases, to successively reduce the iron oxides to lower stages of oxidation; and finally to metallic iron. An even more specific object relates to such process providing a series of staged reaction zones wherein a significant portion of hydrogen is used as the reducing gas.

These and other objects are achieved in accordance with the present invention which contemplates the use of a novel class of agents or additives added to, injected within, or otherwise mixed or contacted with fluidized oxidic iron ore in a reduction process, which even in very minor or minute concentrations, inhibit or prevent bogging of the particulate ore. It has thus been found that small quantities of sulfur compounds, or mixtures the-reof, can be directly added or injected into a fluidized iron ore reduction bed, or admixed wit-h the reducing gas, to inhibit and in some instances to entirely prevent bogging.

The reasons for the effectiveness of these added agents in inhibiting or preventing bogging are not fully understood. While applicants do not desire to be bound by apy theory of mechanism, it is believed that the novel additives of this invention, chemically react with, alter, or otherwise poison the nodular growths or active sites on the surface of the individual iron ore particles which form as temperature is increased. Because of this poisoning effect, the normal tendency of the particles to stick or bridge together upon physical contact one particle with another is inhibited or eliminated.

While concentrations of additives on the order of about 200 parts per million parts of reducing gas, will inhibit bogging to some extent, it is generally preferable to employ concentrations ranging from at least about 0.5 to about 3.0 percent, based on the volume of the reducing gas. Greater concentrations can be used if desired but, except in the instance of very stubborn ores, such amounts of additives are not required. In most instances it is found suitable to employ concentrations ranging from about 0.5

to about 1.5 percent of. the additive, based on the volume of reducing gas.

Additives suitable for use in accordance with the present invention, whether added to the process ab initio or generated in situ, are the divalent sulfur compounds, or sulfides, characterized by the following formula wherein R and R are the same or different and can be hydrogen or monovalent organic radicals, e.g., hydrocarbon and radicals, such as alkyl, alkenyl, alkynyl, aryl, arylalkyl, aralkyl and the like, and S is the chemical symbol for sulfur. The organo radicals can be substituted or unsubstituted, and where substituted the hydrogen of the radical may be replaced by halogen, nitro groups, amino groups, carbonyl groups and the like; or, the radical, where of ring structure, can be ring substituted to form a heterocyclic radical. The carbon of a ring can be substituted, for example, by sulfur, nitrogen, or the like. Preferably, an organo radical should contain no more than about ten carbon atoms, and more preferably about six carbon atoms. Exemplary of these classes of compounds are methyl sulfide, n-propyl sulfide, ethyl n-propyl sulfide, cetyl isoamyl sulfide, bis(trichloromethyl)sulfide, allyl benzyl sulfide, phenyl trichloromethyl sulfide, l-naphthyl phenyl sulfide, 9-methyl mercaptophenanthrene, 3-(ethylmercapto)thiophene, 3 -ethylcyclohexanethiol, 8-quinolinethiol and the like.

Preferably, the sulfides contain no more than one monovalent organo radical, and most preferably R and R are both hydrogen. Exemplary of such compounds are methyl mercaptan, isopropyl mercaptan, n-amyl mercaptan, allyl mercaptan, 3-acridinemercaptan, a-methyl benzyl mercaptan, Z-naphthalene thiol and the like. Mixtures of any of such compounds with other substances or with each other are suitable. Many commercial mixtures and naturally occurring materials which provide these compoundse.g., shale and shale oil-can also be added, preferably after pulverization where solids are used, to the process to gen-' erate the desired compounds in situ.

Hydrogen sulfide is an outstanding compound because of its availability, its readily usable form, and the effectiveness thereof in extremely small concentrations.

Other divalent sulfur compounds are also suitable. These include such compounds as the polysulfides, especially the disulfides illustrative of which are carbon disulfide, niethylethyl disulfide, Z-fenchanyl methyl disulfide,

ert-butyl-Z-naphthyl disulfide, 2-(o-nitrophenyldithio) benzothiazole, and the like.

In a particularly'preferred embodiment according to this invention, oxidic ores or iron oxides solids particles are contacted with upwardly flowing hydrogen-containing gases and a plurality of staged zones are provided. The zones contain fluidized beds operated at varying temperatures and the ore is at different stages of reduction. Also, the reducing gas in contact with the beds is at a different stage of oxidation within the zones. There is provided, in accordance with such embodiment, one or more ferric reduction zones operated at temperatures ranging from about 1000 F. to about 1800 F. and one or more ferrous reduction zones operated at temperatures ranging from about 1300 F. to about 1500 F. The sulfide compounds are added to the ferrous reduction zone wherein the tendency to bog is extremely acute.

The following nonlimiting examples and pertinent demonstrations bring out the more salient features and provide a better understanding of the invention.

A large quantity of raw Carol Lake ore is pulverized in a ball mill, to a particle size ranging from about 75 to 210 microns, and divided into several like portions. This ore is one well known as possessing a severe tendency to bog.

A portionof the ore is charged into a fluidized iron ore reactor or reduction process wherein is provided a series of four staged fluidized zones, two ferric reduction zones and two ferrous reduction zones. The ore is fluidized by an upwardly flowing gas initially sixty percent hydrogen and forty percent nitrogen. The gas flows from a zone containing an iron ore at a lower level of oxidation to the next higher level of oxidation, i.e., from the bottom to the top of the reactor. In the top ferric zone the partially oxidized gas is burned with air to provide heat to the various reduction stages and the reduced ore moves from the top to the bottom of the reactor from one stage of reduction to the next. The ferric reduction stages, wherein ferric oxides are reduced essentially to magnetic oxides of iron, are operated at 1300 F. as were the ferrous reduction stages wherein the ferrous oxide is reduced, in the final stage to provide 94 percent metallization.

Pursuant to operating at such conditions, the ferrous reduction beds shows sign of bogging within about ten minutes and are severely and totally bogged in only twenty minutes of continuous operation.

EXAMPLE I The foregoing demonstration is repeated in precise detail employing a second portion of the ore except in this instance one percent of hydrogen sulfide, based on the volume of the gas feed, is added to and continuously charged into the ferrous reduction zone. At the end of a fifty-five minute period there is only slight evidence of bogging or tendency toward bogging. The beds appeared normal and the process functioned normally in every way prior to this time. The improvement is thus at least 500 percent improvement over the foregoing demonstration, and clearly evidences the advantages of the present process.

EXAMPLE II When Example I is repeated with another portion of ore at a temperature of 1400 F. and hydrogen sulfide is added in three percent concentration, there is yet no bogging or tendency toward bogging at the end of a significantly longer period.

EXAMPLE III When the conditions of operation of the process of Example 11 are repeated and the same amount of benzyl mercaptan is injected into the process, there is again little evidence of bogging at the end of the period.

EXAMPLES IV-VII When Example I is repeated except that phenyl sulfide, 2 naphthyl phenyl sulfide, 3-(ethylmercapto)thiophene and 1,4-bis(ethylmercapto)benzene, respectively, are successively added ot the process in 0.5, 1.5 and 3.0 percent concentrations, significantly good benefit-s are also obtained. The tendency to bog is considerably reduced and operating time is significantly extended in each instance.

It has been concluded and firmly established that the sulfur compounds of this invention must be present in admixture or solution with the reducing gases, or in physical admixture with the ore at the time of reduction to provide benefits, whether added ab initio or generated in situ from an added material capable of producing such compounds.

Thus, it has been found that the bound sulfur content of the original ore, where chemical analysis shows the presence of sulfur, provides no benefits toward elimination or reduction of bogging. In other words, high sulfur content ores pose bogging problems as severe as, and occasionally problems even more severe, than ores containing little or no sulfur. Thus, e.g., a Hammersly ore which chemical analysis shows to contain 0.043 percent sulfur when treated at 1300 P. will not bog when fluidized by and contacted with a 60:40 mixture of hydrogenmitrogen for a period of 4 /2 hours. The same is true of certain other ores which analysis shows to contain even less or only slightly more sulfur. In sharp contrast, however, a Santa Ines ore reduced under precisely the same conditions will bog in 58 minutes, though analysis shows the sulfur content to be 3.22 percent. There are other ores containing high sulfur content which also present bogging problems equal- 1y as severe. There is then no relationship between bound sulfur and elimination or inhibition of bogging.

It is apparent that certain modifications and changes can be made in the present process without departing the spirit and scope of the invention. The key and novel feature of the invention is the use of small and minor portions of divalent sulfur compounds directly added to, injected within, premixed, or otherwise physically admixed with the reducing gases in contact with the oxidic iron ores which are subjected to reduction in a fluidized process.

Such compounds in contact with the fluidized ore at the time of reduction provide benefits, whether added ab initio or generated in situ from an added material itself capable of providing such compounds.

Having described the invention, what is claimed is:

1. In a process for the production of sponge iron from oxidic iron ores wherein the iron ore in particulate form is fed into the process and fluidized within a bed and reduced by a stream of gas at temperatures ranging from about 1000 F. to about 1800 F. the improvement comprising providing within the reducing gas in contact with the fluidized bed to inhibit bogging, at least about 200 parts, per million parts of reducing gas, to about 3 percent, based on the volume of the reducing gas, of a divalent sulfur compound characterized by the formula wherein R and R are selected from hydrogen and monovalent organo radicals.

2. The process of claim 1 wherein the divalent sulfur compound is provided in quantities ranging from about 0.5 to about 3 percent, based on the volume of reducing gas.

3. The process of claim 1 wherein the divalent sulfur compound is provided in quantities ranging from about 0.5 to about 1.5 percent, based on the volume of reducing gas.

4. The process of claim 1 wherein the R and R moieties of the divalent sulfur compound contains no more than about ten carbon atoms.

5. The process of claim 1 wherein the temperature ranges from about 1300 F. to about 1600 F., and the divalent sulfur compound is hydrogen sulfide.

6. In a process for the production of sponge iron from oXidic iron ores wherein the iron ore in particulate form is fed into the process and fluidized by a stream of gas within a series of staged zones containing fluidized beds, including a ferric reduction zone and a ferrous reduction zone, and reduced at elevated temperatures ranging from 1000" F. to about 1800 F., the improvement comprising providing within the reducing gas in contact with the fluidized ferrous reduction bed, to inhibit bogging, at least about 200 parts, per million parts of reducing gas, to about 3 percent, based on the volume of the reducing gas, of a divment sulfur compound characterized by the formula wherein R and R are selected from hydrogen and monovalent organo radicals 7. The process of claim 6 wherein the temperature of the fluidized ferrous reduction bed ranges from about 1300 F. to about 1500 F., and the divalent sulfur compound is hydrogen sulfide.

8. In a process for the production of sponge iron ores wherein the iron ore in particulate form is fed into the process and fluidized by a stream of gas within a series of staged zones containing fluidized beds, including a ferric reduction zone and a ferrous reduction zone, and reduced at elevated temperatures ranging from about 1000 F. to about 1800 F., the improvement comprising providing within the reducing gas in contact with the fluidized ferrous reduction bed, to inhibit bogging, at least about 0.5 to about 3.0 volume percent, and higher, of a divalent sulfur compound characterized by the formula wherein R and R are selected from hydrogen and monovalent organo radicals.

9. The process of claim 8 wherein the divalent sulfur compound is provided to the ferrous reduction zone is in concentrations ranging from about 0.5 to about 1.5 percent, based on the volume of the reducing gas.

10. The process of claim 8 wherein the R and R moieties of the divalent sulfur compound contain no more than 10 carbon atoms.

11. The process of claim 8 wherein the temperature of the fluidized ferrous reduction bed ranges from about 1300 F. to about 1500 F., and the divalent sulfur compound is hydrogen sulfide.

12. In a process for the production of sponge iron by direct reduction of particulate oxidic iron ores the combination comprising fluidizing iron oxides solids partcles with upwardly flowing hydrogen-containing gases, providing a plurality of staged fluidized reduction zones including a ferric reduction zone operated at temperatures ranging from about 1000 F. to about 1800" F. and a ferrous reduction zone operated at temperatures ranging from about 1300 F. to about 1500 F., adding within the reducing gas to the ferrous reduction zone at least about 200 parts, per million parts of reducing gas,'to about 3 percent, based on the volume of the reducing gas, of a divalent sulfur compound characterized by the formula R -s-R,

wherein R and R are selected from hydrogen and monovalent organo radicals, while reducing the oxides to lower states of oxidation.

13. In a process for the production of sponge iron by direct reduction of particulate oxidic iron ores the combination comprising fluidizing iron oxides solids particles with upwardly flowing hydrogen-containing gases, providing a plurality of staged fluidized reduction zones including a first ferric reduction zone wherein ferric oxide is reduced to a lower state of oxidation and hydrogen is burned with an oxygen-containing gas to provide heat for the process and to maintain an operating temperature of from 1300 F. to about 1600 F. in the ferric reduction zone, providing a plurality of ferrous reduction zones operated at from about 1300 F. to about 1500 F. wherein ferrous oxide is reduced to metallic iron, and providing to the said ferrous reduction zones from about 0.5 to about 1.5 percent, and higher, based on the volume of reducing gas, of a divalent sulfur compound characterized by the formula R S-R wherein R and R are selected from hydrogen and monovalent organo radicals.

14. The process of claim 13 wherein the divalent sulfur compound is hydrogen sulfide.

References Cited UNITED STATES PATENTS 2,550,609 4/1951 Slater -35 2,758,021 8/1956 Drapeau et al. 75-26 X 2,835,557 5/1958 West et al. 75-26 3,019,100 1/ 1962 Robson 75-26 3,022,156 2/1962 Eastman 75-35 X 3,062,639 11/1962 Sterling 75-26 3,246,978 4/ 1966 Porter et al 75-26 DAVID L. RECK, Primary Examiner. HYLAND BIZOT, Examiner. H. TARRING, Assistant Examiner. 

1. IN A PROCESS FOR THE PRODUCTION OF SPONGE IRON FROM OXIDIC IRON ORES WHEREIN THE IRON ORE IN PARTICULATE FORM IS FED INTO THE PROCESS AND FLUIDIZED WITHIN A BED AND REDUCED BY A STREAM OF GAS AT TEMPERATURES RANGING FROM ABOUT 1000*F. TO ABOUT 1800*. THE IMPROVEMENT COMPRISING PROVIDING WITHIN THE REDUCING GAS IN CONTACT WITH THE FLUIDIZED BED TO INHIBIT BOGGING, AT LEAST ABOUT 200 PARTS, PER MILLION PARTS OF REDUCING GAS, TO ABOUT 3 PERCENT, BASED ON THE VAOLUME OF THE REDUCING GAS, OF A DIVALENT SULFUR COMPOUND CHARACTERIZED BY THE FORMULA 